Fix stack overflow exception in CSharpResolver

ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj

@@ -94,6 +94,7 @@
     <None Include="TestCases\ILPretty\GuessAccessors.il" />
     <None Include="TestCases\ILPretty\Issue2260SwitchString.il" />
     <None Include="TestCases\ILPretty\Issue3442.il" />
+    <None Include="TestCases\ILPretty\Issue3466.il" />
     <None Include="TestCases\ILPretty\MonoFixed.il" />
     <None Include="TestCases\Correctness\NonGenericConstrainedCallVirt.il" />
     <None Include="TestCases\ILPretty\UnknownTypes.cs" />
@@ -135,6 +136,7 @@
     <Compile Include="TestAssemblyResolver.cs" />
     <Compile Include="TestCases\ILPretty\Issue3421.cs" />
     <Compile Include="TestCases\ILPretty\Issue3442.cs" />
+    <Compile Include="TestCases\ILPretty\Issue3466.cs" />
     <Compile Include="TestCases\ILPretty\MonoFixed.cs" />
     <Compile Include="TestCases\Pretty\Comparisons.cs" />
     <Compile Include="TestCases\Pretty\GloballyQualifiedTypeInStringInterpolation.cs" />

ICSharpCode.Decompiler.Tests/ILPrettyTestRunner.cs

@@ -219,6 +219,12 @@ public async Task Issue3442()
 			await Run();
 		}
 
+		[Test]
+		public async Task Issue3466()
+		{
+			await Run();
+		}
+
 		[Test]
 		public async Task Issue2260SwitchString()
 		{

ICSharpCode.Decompiler.Tests/TestCases/ILPretty/Issue3466.cs

@@ -0,0 +1,14 @@
+namespace ICSharpCode.Decompiler.Tests.TestCases.ILPretty
+{
+	public class Issue3466<T>
+	{
+		public static implicit operator Issue3466<T>(T t)
+		{
+			return null;
+		}
+		public static bool M(Issue3466<object> x)
+		{
+			return x != null;
+		}
+	}
+}

ICSharpCode.Decompiler.Tests/TestCases/ILPretty/Issue3466.il

@@ -0,0 +1,49 @@
+.assembly extern System.Runtime
+{
+	.publickeytoken = (B7 7A 5C 56 19 34 E0 89 )                         // .z\V.4..
+	.ver 4:0:0:0
+}
+
+.assembly Issue3466
+{
+	.hash algorithm 0x00008004 // SHA1
+	.ver 0:0:0:0
+}
+
+.class public auto ansi beforefieldinit ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3466`1<T>
+	extends [System.Runtime]System.Object
+{
+	.method public hidebysig specialname static 
+		class ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3466`1<!T> op_Implicit (
+			!T t
+		) cil managed 
+	{
+		.maxstack 8
+
+		IL_0000: ldnull
+		IL_0001: ret
+	}
+
+	.method public final hidebysig static bool M(class ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3466`1<object> x) cil managed 
+	{
+		.maxstack 8
+
+		IL_0000: ldarg.0
+		IL_0001: brtrue.s IL_0004
+		IL_0002: ldc.i4.0
+		IL_0003: br.s IL_0005
+		IL_0004: ldc.i4.1
+		IL_0005: ret
+	}
+
+	.method public hidebysig specialname rtspecialname 
+		instance void .ctor () cil managed 
+	{
+		.maxstack 8
+
+		IL_0000: ldarg.0
+		IL_0001: call instance void [System.Runtime]System.Object::.ctor()
+		IL_0006: ret
+	}
+
+}

ICSharpCode.Decompiler/CSharp/Resolver/CSharpResolver.cs

@@ -805,7 +805,7 @@ public ResolveResult ResolveBinaryOperator(BinaryOperatorType op, ResolveResult
 					}
 					if (op == BinaryOperatorType.Equality || op == BinaryOperatorType.InEquality)
 					{
-						if (lhsType.IsReferenceType == true && rhsType.IsReferenceType == true
+						if (lhsType.IsReferenceType == true && rhsType.IsReferenceType == true && lhsType.Kind != TypeKind.Null && rhsType.Kind != TypeKind.Null
 							&& (conversions.IdentityConversion(lhsType, rhsType)
 								|| conversions.ExplicitConversion(lhsType, rhsType).IsReferenceConversion
 								|| conversions.ExplicitConversion(rhsType, lhsType).IsReferenceConversion))